If a tsunami were to hit California it would have devastating effects, according to a new report from the US Geological Survey.

Were a major earthquake to strike off the coast of the Golden State, the ensuing tsunami would close major seaports, flood at least one major airport and lead to mass evacuations, according to the USGS.

The damage and lost economic activity could number in the billions, according to the agency.

Severe damage: The tsunami caused by the 2011 Japan earthquake caused fishing boats in Crescent City, CA to be run ashore - over 4,800 miles away

Were an earthquake similar to the monster 9.1 earthquake that struck in 2011 off the coast of Japan - causing extensive damage and a nuclear meltdown – to strike off the coast of California, its nuclear power plants would be safe, but not much else would be.

At least 750,000 people would need to be immediately evacuated from coastal areas such as Newport Beach, with at least 90,000 of them being tourists or visitors, according to the USGS, causing untold amounts of economic activity to be brought to a halt.

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The posts of Los Angeles and Long Beach would be closed for at least a handful of days, leading to a loss of at least $1.2billion, if not more, according to the USGS.

At least one-third of the boats docked in the state’s marinas could be damaged or completely sunk, with liabilities running upwards of $700million, said the agency.

Run!: People relaxing on Newport Beach would have to evacuate if a tsunami were to hit California

Oakland International Airport would be flooded and need to be closed until the water subsided, with any necessary rebuilding adding to the liability total.

Despite these dire predictions, the state could be worse-off.

‘The good news is that three-quarters of California's coastline is cliffs, and thus immune to the harsher and more devastating impacts tsunamis could pose,’ Lucy Jones, USGS Science Advisor for Risk Reduction, said in a release announcing the study.

There is one caveat though, ‘the one-quarter at risk is some of the most economically valuable property in California,’ Jones added.

The study began after the tsunami triggered by the 2011 earthquake damaged Crescent City, a commercial fishing village just south of the Oregon state line.

It was completed to provide ‘a clearer understanding on how tsunamis function and their potential impacts,’ and is meant to be a companion to a previous study examining the ‘consequences of a probable major earthquake on the southern San Andreas Fault,’ according to the agency.